"William, that is a 1977 "
"William, that is a 1977 "A" model Mariner built by Yamaha for Merc.
The A models were short lived. Yamaha discontinued the model (due to technical advances) in 1979 after two years of production. They ran out the remainder of the parts in stock by continuing to produce the Mariner version for an additional two years - the last one came off the production line in 1981.
Parts are super difficult to find for this particular model and unfortunately they are nothing like the 40 horse "C" models which were very prolific and were produced up until the early 1990's.
If it's running well, take very good care of it. It was a well built engine, but it's very much an orphan now...."